Which muscle type is responsible for involuntary movements and is not striated?

Smooth muscle is the type of muscle responsible for involuntary movements and is characterized by a lack of striations, which means it does not have the distinct striped appearance seen in striated muscle types. This muscle type is found in various internal structures, such as the walls of blood vessels, the gastrointestinal tract, and the respiratory passages.

Smooth muscle contractions are typically slow and sustained, allowing for functions like regulating blood flow and aiding digestion without conscious control, distinguishing it from skeletal muscle, which is primarily under voluntary control and striated, and cardiac muscle, which, although involuntary and striated, has a different structure and function tailored to the heart. Thus, smooth muscle's unique properties make it essential for many vital physiological processes that occur without the need for conscious thought or control.